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Inherited megaloblastic anemia caused by a constitutional malabsorption of vitamin B12.

Defect of Enterocyte Intrinsic Factor Receptor; Enterocyte Cobalamin Malabsorption; Imerslund-Grasbeck Syndrome; Imerslund-Najman-Grasbeck Syndrome; Juvenile Pernicious Anemia due to Selective Intestinal Malabsorption of Vitamin B12 with Proteinuria.

Internationally, the incidence of megaloblastic anemia in childhood is not established; however, 29 cases have been reported in the Middle East between 1960 and 1998.

Autosomal recessive with multiple nonallelic forms. Gene map locus is 10p12.1.

Megaloblastic anemia secondary to B12 malabsorption, with proteinuria. The disease is caused by a selective defect between the attachment of B12 to the ileal cell surface and binding to transcobalamin II or absence of functional receptor (cubilin); it is not influenced by the administration of intrinsic factor. Renal function studies are normal.

Bone marrow exam shows megaloblastic anemia. The Schilling test, which assesses cobalamin absorption both with and without exogenous intrinsic factor, is abnormal. Urinalysis reveals proteinuria despite otherwise normal renal function studies.

Megaloblastic anemia that responds to parenteral cobalamin administration. Proteinuria. This condition has been associated with dolichocephaly, confusion, dementia, generalized paresthesias, and sensory deficits.

Mandatory to obtain a complete blood cell (CBC) count, vitamin B12 plasma level, and urinary protein level.

Consider postponing elective surgery in face of untreated anemia. In case of surgical emergency, complete type and crossmatch for blood must be obtained.

Theoretically, nitrous oxide should be avoided because it reduces the activity of the vitamin B12-dependent enzymes methionine synthetase and thymidylate synthetase.

Other causes of megaloblastic anemia by deficiency of either vitamin B12 or folinic acid:

Vitamin B12 Deficiency: Impaired absorption (insufficient release of vitamin B12 from protein, intrinsic factor deficiency, chronic pancreatic or intestinal disorders, parasitoses) or inadequate utilization (defective enzymes, lack of transcobalamin II, chronic exposure to nitrous oxide).

Folic Acid Deficiency: Prematurity, insufficient dietary intake, alcoholism, intestinal derivation, tropical sprue, treatment with sulfasalazine or folic acid antagonists such as methotrexate, hemodialysis.

Ben-Ami M: Imerslund syndrome with dolichocephaly. Pediatr Hematol Oncol 7:177, 1990.  [PubMed: 2169845]
Gueant JL, Chery C, Namour F, et al: Decreased affinity of urinary intrinsic factor-cobalamin receptor in a case of Grasbeck-Imerslund syndrome. Gastroenterology 116:1274, 1999.  [PubMed: 10220529]

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